The car is a 2005 180K C class saloon. My problem relates to a 'Bonking' noise from the back of the car which is just 4 years old and has covered 17,000 miles. I first of all thought it was the spare wheel or the floor cover but I have now eliminated these. I think it actually comes from the rear off side. It is only noticable when going over a sharp bump or manhole cover. It may be just a figment of my imagination but the noise seems to disappear for a short time after the vehicle has been on a ramp with the wheels hanging down as was the case during it's recent MOT. Any ideas?